In the prior art, the engine brake technology is well known. Engine braking can be achieved by temporarily converting the engine into a compressor. In the conversion process, the fuel is cut off, and the exhaust valve is opened near the end of the compression stroke of the engine piston, thereby allowing the compressed gases (being air during braking) to be released. The energy absorbed by the compressed gas during the compression stroke of the engine cannot be returned to the engine piston in the subsequent expansion stroke, but is dissipated by the engine exhaust and cooling systems. The above process finally results in an effective engine braking and the slow-down of the vehicle.
The engine brake includes Compression Release Brake and Bleeder Brake. In an engine using the Compression Release Brake, the exhaust valve is opened near the end of the compression stroke of the engine piston, and is closed after the compression stroke (during the early stage of the expansion or power stroke, prior to the normal opening of the exhaust valve). In an engine using the Bleeder Brake, the exhaust valve is kept slightly open with a constant lift in addition to the normal exhaust valve opening during a part of the engine cycle (Partial Cycle Bleeder Brake) or during the non-exhaust stroke (i.e. the intake stroke, the compression stroke and the expansion or power stroke) of the engine cycle (Full Cycle Bleeder Brake). The main difference between the Partial Cycle Bleeder Brake and the Full Cycle Bleeder Brake is that the former does not open the exhaust valve during most of the intake stroke.
An example of a conventional engine brake device is a hydraulic-type engine brake provided by Cummins in the disclosure of U.S. Pat. No. 3,220,392 in 1965. In the conventional engine brake, a mechanical input is transmitted to an exhaust valve to be opened through a hydraulic circuit. A master piston reciprocating in a master piston bore is located in the hydraulic circuit. The reciprocating motion comes from the mechanical input of the engine, such as the motion of the engine's fuel injection cam or the neighboring exhaust cam. The motion of the master piston is transmitted through hydraulic fluid to a slave piston located in the hydraulic circuit, causing the slave piston to reciprocate in a slave piston bore. The slave piston acts, directly or indirectly, on the exhaust valve, thereby generating the valve event for the engine braking operation.
The engine brake device disclosed by Cummins is a bolt-on accessory that fits above the engine. In order to mount the engine brake, a spacer needs to be provided between the cylinder and the valve cover, such that the height, weight and cost of the engine are additionally increased. Obviously, the solution to the above problems is to integrate the components of the braking device in the existing components of the engine, such as in the rocker arm or in the valve bridge of the engine, thereby forming an integrated brake. The integrated engine brakes in the prior art have the following forms.
1. Integrated Rocker-Arm Brake
An integrated compression release engine brake system was disclosed by Jonsson in U.S. Pat. No. 3,367,312 in 1968. The brake system is integrated in a rocker arm of the engine, and a plunger or a slave piston is positioned in a rocker-arm cylinder arranged at one end, close to an exhaust valve, of the rocker arm and is locked in a protruding position hydraulically, such that a cam motion can be transmitted to one exhaust valve (there is only one valve per cylinder in an early engine) to generate the engine braking operation. As disclosed by Jonsson, a spring is provided for biasing the plunger outward from the cylinder to be in continuous contact with the exhaust valve so as to allow the cam-actuated rocker arm to operate the exhaust valve in both the power and braking modes. In addition, a control valve is used to control the flow of pressurized fluid to the rocker-arm cylinder so as to realize selective switching between a braking operation and a normal power operation.
A different integrated rocker-arm brake was disclosed by the Mack Truck Company of the United States in U.S. Pat. No. 3,786,792 in 1974. The braking piston of the brake system is positioned in a rocker-arm cylinder arranged at one end, close to a push rod, of the rocker arm and is hydraulically locked in the protruding position, such that the motion of the cam is transmitted to an exhaust valve (there is only one valve per cylinder in an early engine) to produce the engine braking operation. A conventional cam lobe and a braking cam lobe are integrated in the above cam. The brake control valve mechanism (a combination of a funnel-shaped plunger valve and a one-way ball valve) in the above brake system was widely used after its disclosure.
Another integrated rocker-arm brake is disclosed by the Jacobs Company (JVS) of the United States in U.S. Pat. No. 3,809,033 in 1974. The braking piston of the brake system is positioned in a rocker-arm cylinder arranged at one end, close to the valve bridge, of the rocker arm, and is movable between a non-braking position and a braking position. In the braking position, the braking piston is hydraulically locked in a protruding position, such that the cam motion is transmitted to the valve bridge to open two exhaust valves (the engine has two valves per cylinder) for producing the engine brake operation. The braking system uses two separate oil passages, one for supplying oil to the brake, and the other being a conventional engine lubrication oil passage.
An integrated rocker-arm brake system for an overhead cam four-valve engine was disclosed by Sweden's Volvo Company in U.S. Pat. No. 5,564,385 in 1996, which is very similar in both structure and principle to the integrated rocker-arm brake disclosed by Jacobs Company (JVS) in U.S. Pat. No. 3,809,033 in 1974. The hydraulic braking piston is positioned in a rocker-arm cylinder arranged at one end, close to the valve bride, of the rocker arm and is movable between a non-braking position and a braking position and forms a gap in the engine air valve system. Oil with a certain pressure is supplied to the braking piston by a pressure control valve to fill the gap in the rocker arm so as to form a hydraulic linkage. The engine braking system adopted the combined structure having a funnel-shaped plunger valve and a one-way ball valve and added an overload pressure relief mechanism, and an oil supply device for providing dual oil pressures via a single oil passage, wherein a low oil pressure (below the engine lubricating oil pressure) is used for the engine lubrication, and a high oil pressure (equal to the engine lubricating oil pressure) is used for the engine brake. During engine braking, the braking piston drives the valve bridge to open the two exhaust valves simultaneously.
Another new integrated rocker-arm brake was disclosed by the Mack Truck Company of the United States in U.S. Pat. No. 6,234,143 in 2001, which is quite different from the technology disclosed in U.S. Pat. No. 3,786,792 in 1974. First of all, an Exhaust Gas Recirculation (EGR) cam lobe was added to the integrated cam formed with the conventional cam lobe and the braking cam lobe, which facilitates improving the braking power. Secondly, the engine with a single valve per cylinder is changed into an engine with dual valves per cylinder, and a valve bridge (an air valve bridge or a cross arm) was added. Further, the braking piston in the rocker-arm piston bore is moved from the push rod side to the valve bridge side, and is located above the exhaust valve (an inner valve) next to the rocker-arm shaft. During braking, the braking piston opens one exhaust valve via a braking top block or by a direct action on the valve bridge. However, since only one valve is opened for braking, the valve bridge is in an inclined state and an asymmetric load is generated on the valve bridge and the rocker arm. Furthermore, the braking valve (the inner valve) lift profile is greater than the non-braking valve (an outer valve) or the conventional valve lift profile (larger opening and later closing).
An integrated rocker-arm brake system having a valve lift reset mechanism was disclosed by Cummins Engine Company in U.S. Pat. No. 6,253,730 in 2001 to resolve the problems of the one-valve (the inner valve) braking, such as the asymmetric load and the braking valve (the inner valve) lift profile being greater than the non-braking valve (the outer valve) or the conventional valve lift profile (larger opening and later closing). The valve lift reset mechanism resets or retracts the braking piston in the rocker arm before the braking valve reaches its peak valve lift, which allows the braking valve to return to the valve seat before the start of the main valve action, such that the valve bridge returns to the horizontal position, and the rocker arm can open the braking valve and the non-braking valve evenly, thereby eliminating any asymmetric load.
However, there are a lot of problems with resetting the engine braking system before the braking valve reaching its peak valve lift. Firstly, during engine braking, both the opening time and the lift magnitude of the braking valve are very short, thus the time for resetting is very limited. Secondly, the resetting occurs when the engine braking load is close to the maximum (i.e. the top dead center of the compression stroke), thereby causing the reset valve of the valve lift reset mechanism to bear a high oil pressure or a large load. Thus, the engine brake resetting timing is essential. If the resetting occurs too early, the loss of braking valve lift is too much (causing a lower valve lift and the valve to be closed too early), which may reduces the braking performance. If the resetting occurs too late, the braking valve can not be closed before the start of the main valve action, which may results in an asymmetric load. Tests show that the integrated rocker-arm brake cannot work properly at high engine speeds, because the resetting time is too short, the resetting height is too small, and the load or pressure on the reset valve is very high.
2. Integrated Valve Bridge Brake
An example of a conventional integrated valve bridge brake was disclosed by Calvin in U.S. Pat. No. 3,520,287 in 1970. The entire valve bridge is set on a central guide rod. The guide rod is provided with an internal brake oil passage and a control valve. An upper portion of the guide rod acts as a braking piston, the valve bridge slides along the braking piston through a piston bore in the valve bridge. The disadvantage of this apparatus is that there is always a large relative motion between the braking piston and the piston bore in the valve bridge.
An improved valve bridge brake mechanism was disclosed by Sickler in U.S. Pat. No. 4,572,114 in 1986. A dedicated braking piston is housed in a piston bore opened upward at the center of the valve bridge, such that the relative motion between the braking piston and the valve bridge is greatly reduced. The valve bridge brake mechanism was designed for a four-stroke engine, but each engine cycle produces two compression release braking events.
Recently, the Jacobs Company (JVS) of the United State designed and manufactured a valve bridge brake device (see U.S. Publication No. 20050211206 and No. 20070175441) for Hyundai Truck Company in South Korea. Wherein, a valve lift reset mechanism was added to the valve bridge brake mechanism disclosed by Sickler in U.S. Pat. No. 4,572,114 in 1986. But similar to the valve lift reset mechanism disclosed by Cummins Engine Company in U.S. Pat. No. 6,253,730 in 2001, the reset valve of the valve lift reset mechanism is located in the exhaust valve actuator (in the rocker arm for Cummins and in the valve bridge for JVS), while the reset top block or the reset rod is located on the engine, such that it is very difficult to ensure the height and timing for resetting the braking valve lift, and it is also not convenient for installation, transportation and adjustment.